The present invention is directed to a wire dot printer, and, in particular, to a wire dot printer having a matrix of wire ends for carrying inks of different colors to effect multicolor printing on a recording medium such as paper.
For printing in different colors, an impact color printer has been proposed and put into use which employs a ribbon having strips which are differently colored either longitudinally or transversely. This type of impact color printer can print characters in only one color while the print head thereof is scanning the paper in a single scanning stroke. When it is necessary to print different colors on a single line, the print head is required to scan the same line in as many strokes as there are colors to be printed, resulting in a greatly reduced printing speed. The service life of the overall ribbon is governed by that of the color strip thereof which is most frequently used. With the prior art impact color printer, more colors than colors available on the ribbon can be printed by printing a number of juxtaposed colors on the same dot. However, the ink previously printed on the dot tends to be transferred to ribbon strips of other colors, with the result that inks of different colors will be mixed together on the ribbon as the ribbon is frequently used.
Two of the inventors of the present application together with two other inventors have proposed, in copending application Ser. No. 274,322 filed June 16, 1981, now U.S. Pat. No. 4,456,393, issued June 26, 1984 and entitled "Wire Dot Printer" incorporated herein by reference as though fully set forth, a wire dot printer having a matrix of wire ends for carrying ink to effect printing. The wire dot printer disclosed in that application is capable of supplying an appropriate amount of ink to the wire ends for performing stable printing of high quality. The present invention has been made and developed in connection with the invention disclosed in the above referred to copending application but provides a wire dot printer capable of multicolor printing.
The wire dot printer disclosed in the prior copending application employes two tubes for supplying ink to a print head and for collecting excess ink. To convert that type of wire dot printer into a color printer which utilizes three differently colored inks, a total of six ink supply and collection tubes would be required to connect the respective ink tanks for the three inks to a print head, the tubes being coupled to predetermined portions of the print head. Accordingly, such a color printer would be cumbersome and difficult to assemble.
It is important in wire dot printers utilizing multicolor inks or inks of different colors that provision be made for preventing the inks from being mixed together with each other. To this end, the interior of the print head should have ink passages formed for respective colored inks in a limited space without causing color mixing. Therefore, such a print head is liable to be complex in structure, cumbersome to put together, and less reliable in operation.
With the wire dot printer of the prior copending application, the continued printing operation may result in a deposit of paper dust from the recording paper and ink being spattered from the paper on the end of the print head. As a result, the recording paper tends to become smeared by the deposit of ink and paper dust on the print head. The deposited paper dust may find its way into the ink passage tubes to thereby interfere with proper supply and collection of ink. For color printing with inks of various colors, the deposited paper dust may give rise to capillary attraction causing the inks to become mixed together. The printed characters would thus be of mixed colors, and no proper color printing could be accomplished. Accordingly, it is desired to provide an improved wire dot printer which can print in different colored inks while avoiding the problems described above.